1. Field of the Invention
The present invention relates to a surface acoustic wave (hereinafter referred to as “SAW”) apparatus, in particular, an SAW apparatus used for a transmit-receive demultiplexer (duplexer) of a communications equipment requiring miniaturized, high electric power resistance.
2. Description of Related Art
Recently, a SAW filter has been used for various communications equipment.
Since the SAW filter has steep filter characteristics and excellent features such as exceptional mass-production quality, it has been often used for, in particular, mobile communications equipment.
In place of a conventionally used dielectric filter, the SAW filter has also been employed as a filter constituting a duplexer in the mobile communications equipment.
However, since a signal amplified by a power amplifier passes through the duplexer, high electric power of as much as 0.8 to 1.2 W is applied at the time of communication.
When high electric power is applied to an IDT (Inter Digital Transducer) electrode of the SAW filter, a large amount of heat is generated in the IDT electrode and migration of the electrode material is accelerated due to the heat and thus high power durability of the IDT electrode becomes insufficient.
Thus, since high power durability is insufficient in the conventionally used SAW filter, there is a strong demand for the SAW filter having improved high power durability.
For the duplexer, improvement of high power durability and miniaturization has been demanded strongly.
Conventionally, a so-called package-type SAW filter has been used. The package-type SAW filter is produced as follows: an SAW device is mounted on a recessed part of a ceramic package and a pad electrode of the SAW device is connected to a terminal part of the package according to a wire-bonding method, and then the recessed part is hermetically sealed with a cap or the like.
On the contrary, a so-called CSP-type SAW filter has been recently widespread. In the CSP-type SAW filter, the SAW device is flip-chip mounted on a circuit board by actively utilizing CSP (Chip Size Package) technique for miniaturization. In this SAW filter, space and height necessary for wire-bonding in the conventional package-type SAW filter can be reduced.
However, the CSP-type SAW filter has the following problem: Since the face of a piezoelectric substrate on which the IDT electrode is formed is mounted face down on the circuit board, high power is applied and thus it becomes more difficult to radiate heat generated in the IDT electrode. As a result, it is disadvantageous in terms of high power durability.
It is due to the fact that, in the CSP-type SAW filter, heat can be radiated from the face of the piezoelectric substrate on which the SAW device is formed to the circuit board only through conductor bumps with very small cross-sectional areas and thus, it is difficult to ensure effective radiation paths. An object of the present invention is to provide a compact CSP-type SAW filter with excellent high power durability.